For at least regulatory reasons, aviation fuels are well into the process of becoming unleaded fuels. The removal of lead from a fuel, however, has the undesired effect of lowering the knock rating of a fuel. Accordingly, as aviation fuels are in the process of becoming unleaded, the formulation of those fuels must account for the octane reduction from losing lead. The addition of her fuel components is needed.
A common way to improve octane performance is to incorporate into an aviation fuel a high amount of aromatic hydrocarbons. These aromatic hydrocarbons allow the aviation fuel to be unleaded but still meet knock rating requirements. However, the use of significant amounts of aromatic hydrocarbons in the aviation fuel changes the burn efficiency of that fuel and results in increasing formation of smoke during the combustion process. Needless to say, increased amounts of smoke are undesirable in terms of aesthetics and environmental impact. Generally speaking, the higher the amount of aromatic hydrocarbons incorporated into a fuel composition, the higher the amount of smoke that is produced during combustion of that fuel.
Another strategy to improve octane performance is incorporate into an aviation fuel a manganese-containing additive. Manganese additives allow the aviation fuel to be unleaded but still improve the knock rating requirements over an unadditized and unleaded fuel composition.